You are in for a TREAT! Norway is an incredible place to photograph, especially the landscapes but not limited to that, and the Lofoten Islands look to be some of the best of that country.
I haven't been on the Lofotens, merely through part of them on the Hurtigruten (coastal ship) which is expensive but a very useful intro to the area. You can travel just part of the Hurtigruten's route, you don't have to do all of the Bergen-Kirkenes-Bergen route.
Although winter is challenging it's not as bad along the coast as you might expect. The Gulf Stream (warmer water than the Arctic) modifies the local climate significantly. Inland is much colder but don't let that put you off. Summer is a bit disorienting because you tend to go without sleep for days and then collapse in a heap
The Gulf Stream is what makes the winter fishery around the Lofotens so good. Make sure you get lots of pics of the cod (torsk) drying on racks- nice patterns as well as being a distinctive local sight.
If you are going to be there in late autumn/winter, be prepared for the highly spectacular Aurora Borealis. This article http://www.luminous-landscape.com/techniques/aurora-md.shtml
has lots of good advice (spare batteries and good high ISO performance seem top of the list).
And although this is a little further inland, you must visit Lyngen Fjord (both summer and winter)- it's a stunning area. Lyngseidet has a charming timber church (built 1731). All of the villages and towns north of Lyngseidet were burned to the ground in late 1944/early 1945 as the German army retreated before the Russian advance, so Lyngseidet was incredibly lucky. The church (typically for churches in coastal Norway) has a model sailing vessel suspended above the altar. Before oil and gas made Norway rich (late 60s) it was a very poor country and the main occupations in coastal areas were seafaring, fishing and pilotage. Navigating those island- and skerry- ridden waters in winter storms without a weather forecast must have been, well, words fail me. Lots of men didn't come home from the sea. My father grew up in Lyngseidet in the 20s and 30s so I'm seriously biased, but it really is a great part of the world.
If possible try to get acquainted with some locals with boats- maritime photography makes a welcome change from land-based (different subjects, different perspective), and you'll be in an area which is half water anyway. If you're going to be there after about October/November you should be able to ski- you don't have to of course, but it will make getting around far easier. And as others have noted, good clothing for the winter months and camera sealing/protection for the maritime jaunts. Maybe get a sea kayak if you have the skills- that would be one of the best ways to get around the islands. (That's on my bucket list....)
The natural features are of course the principal attraction, but don't ignore modernity. There are some spectacular bridges and tunnels between islands worth some photographic time too. More controversially there is a strong push at the moment for oil and gas exploration off the Lofotens. At the moment Norway's oil and gas comes from other offshore regions. There might be some good opportunities there although I don't know whether the proposals have gone beyond paper submissions. I don't think the local fisherpeople are at all impressed with the prospect.
People say Norway is expensive. They are absolutely right. The best thing to do is research as much as you can from home (lots of useful web sites with English language options if you click on the Union Jack), spreadsheet the trip to the nth degree, then go and have fun and try not to obsess too much about the cost.
One more thing- you'd better like eating fish